The effects of different boundary surface materials on the electron power absorption dynamics in capacitive RF plasmas

Low temperature plasmas are used to modify boundary surfaces, but boundary surfaces affect the plasma, too. Via material specific probabilities for particle absorption, reflection, emission, and conversion such surfaces can change process relevant plasma parameters such as flux-energy distribution functions of electrons and ions. In this work, we demonstrate experimentally how the presence of different wafer materials in capacitive radio frequency plasmas can change the mode of electron power absorption via their different ion induced secondary electron emission coefficients under otherwise identical discharge conditions. Exposing two electrodes made of different materials to the plasma at the same time is found to induce a plasma asymmetry in an otherwise symmetric reactor and the simultaneous presence of different modes of electron power absorption at each electrode. This leads to the generation of a DC self bias as a consequence of this Material Asymmetry. These experimental findings are compared to computational results obtained from Particle in Cell simulations to gain further insights.